1. Field of the Invention
The present invention relates to a photosensitive member having a photoconductive layer which includes at least amorphous silicon.
2. Description of the Prior Art
Photosensitive members of various types have already been proposed. Among other things, attention has been focussed on the application to such photosensitive members of amorphous silicon (hereinafter abbreviated as "a-Si"), amorphous germanium (a-Ge) and amorphous silicon-germanium (a-Si:Ge) which are produced by processes such as glow discharge decomposition and sputtering. This is attributable to the fact that photosensitive members of a-Si, a-Ge and a-Si:Ge are much superior to those of selenium or CdS in heat resistance and abrasion resistance, and also from the viewpoint of environmental pollution.
However, photosensitive members comprising photoconductive layers of a-Si, a-Ge and a-Si:Ge have an insufficiently low dark resistance. Thus they dislay the drawback that they cannot be formed to have a charge retaining function as well. For this purpose, Published Unexamined Japanese Patent Application Sho No. 54-145539 proposes to include oxygen and/or nitrogen in the photoconductive layer of a-Si to improve the dark resistivity. However, this in turn deteriorates its photosensitivity, indicating that the amount of oxygen and/or nitrogen that can be included will inevitably have a limit.
In view of the above, there has been proposed in Published Unexamined Japanese Patent Application SHO No. 57-115551 a photosensitive member which comprises an a-Si photoconductive layer and an a-Si insulating layer formed on the photoconductive layer, the a-Si insulating layer containing a large amount of carbon. However, inclusion of carbon in such a photosensitive member will cause the electrophotographic characteristic to vary a great deal, depending on the amount of carbon. For example, when the amount of carbon included in the a-Si insulating layer is relatively small, the layer itself will not be sufficiently high in resistance; also, light fatigue of the layer becomes large and an image blur is caused under highly humid conditions. On the other hand, a large amount of carbon will improve the charge retaining capability and the light transparency of the insulating layer but in turn causes a reduction in the hardness of the layer. Additionally, white dot patterns appear on the image formed due to layer defects in highly humid conditions.
Moreover, when the a-Si photoconductive layer is directly formed on an electro-conductive substrate, patterns such as white dots and pin holes appear on the image obtained. This is attributable to defects in the a-Si photoconductive layer causing leakage of charge carriers. Such defects easily occur depending on the surface condition and contamination of the electro-conductive substrate. Further, charges are easily injected from the substrate, which deteriorate the dark decay characteristic, which in turn causes a reduction in charge retaining ability.